Camera-equipped cellular phones and digital still cameras using a solid-state imaging device such as a CCD or a CMOS have been hitherto known. In such an imaging apparatus, further reductions in the size and the thickness are required, and an imager lens to be incorporated therein whose total length and depth are short is also demended.
Meanwhile, even in small-sized image capture equipment such as camera-equipped cellular phones, a trend is toward their miniaturization as well as a larger number of pixels in their imaging device in recent years, and it is required that even an imager lens to be incorporated therein have a high lens performance for such a solid-state imaging device having a large number of pixels.
In addition, as part of the above-mentioned requirements, even in the small-sized image capture equipment such as camera-equipped cellular phones, there has been a growing demand for optical zoom lenses.
As small- and thin-sized, high-performance zoom lenses, there have been proposed those which, by arranging a prism for folding an optical path in a lens group, have achieved size and thickness reductions in a direction of an incident light axis. For example, zoom lenses disclosed in Japanese Unexamined Patent Application Publications No. 2000-131610 and No. 2004-354869 are known.
The zoom lenses disclosed in the above-mentioned Japanese Unexamined Patent Application Publications No. 2000-131610 and No. 2004-354869 are zoom lenses which have at least a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power, arranged in order from an object side, and which, by arranging a prism for folding an optical path in the first lens group, have achieved a thickness reduction in the direction of the incident light axis.
However, in the zoom lenses of this type, their total optical length is still large, and when considered to be incorporated in small-sized image capture equipment such as a camera-equipped cellular phone, the zoom lenses are inadequate in view of miniaturization. In addition, due to the facts that the number of lenses is large and that a glass material is used in many constituent lenses, there has been an issue such that the manufacturing cost is elevated.
The present invention has been made in view of the issues such as mentioned above, and is intended to provide a zoom lens which has a good optical performance for imaging device having a large number of pixels even with its simple construction, and which can also be small and thin in structure, and an imaging apparatus using the zoom lens.